Blago said the commission in Ponomaryov's presence selected one-fifth of signatures for mandatory check, sending 1,162 for expert examination to the regional department of the Federal Migration Service. The signatories' info should have matched that in the voter registry, she said.

"A total of 317 signatures or 27.3% were found invalid," the election official said.

The commission will meet on February 20 to decide on Ponomaryov's registration. "We're giving time to the candidate to prove that we've erred in our conclusions," Blago said.

Earlier, Ponomaryov stated that if case of registration problems, he would run as a candidate from the Alliance of Greens and Social Democrats.

On January 9, Novosibirsk mayor Vladimir Gorodetsky stepped down following his appointment as deputy Novosibirsk region governor. His deputy Vladimir Znatkov is now acting Novosibirsk mayor.

Russia's third largest city Novosibirsk will hold mayoral election on April 6. There will be one round of voting. Latest reports said 27 candidates have submitted documents for registration.